This invention pertains to a method of improving the storage stability, including resistance to hemolysis and improved viability, of blood products including packed red blood cells (RBCs), platelets and the like. Specifically, a method for extending the viability of these products, as well as their resistance to membrane damaging agents such as radiation, is provided by storing the products in a suspension including an effective amount of L-carnitine or alkanoyl carnitines.
Concern has been steadily growing over both the national, and worldwide blood supplies. Both the integrity and reliability of existing supplies, and the ability to build larger stocks over time, has been brought into question. One reason for this is the relatively short period of storage stability of blood products. Currently, packed RBCs (red blood cell concentrates, or RCC), the dominant form of blood product for transfusions and the like, are limited to a 42-day storage period. After that time, ATP levels fall substantially, coupled with a significant loss of pH, strongly indicating a lack of viability, or, if viable, an extremely short circulation life upon infusion, in vivo whole blood is not stored for substantial periods. For platelets, the current storage period is even shorter, with the standard being 5-days at 22xc2x0C. The difference in storage stability of platelet concentrations (PC) has opposed to RBC, is due to ongoing metabolic reactions in patelets, due in part the presence of mitochondria in PC, and their absence in RBCs. While both blood products show a drop in ATP, coupled with a drop in pH, over time, accompanied by the production of lactic acid, the presence of mitochondria in PC is likely to exacerbate the problem, due to glycolysis.
Simultaneously, concerns over the reliability and integrity of the blood supply have been raised. In particular, contamination of the blood supply with bacteria, or other microbiological agents, has been detected repeatedly. Such a situation is even more severe in countries with less sophisticated collection and storage methods. While agents may be added to collected products to reduce contamination, these are not desirable, given the need to transfuse the products back into recipient patients. One desirable alternative is radiation treatment of the products, after packaging, typically in plasticised vinyl plastic containers. Such radiation treatment would aggravate RBC and perhaps during PC storage, resulting in a diminished function of these cells.
Additionally, a small but growing portion of the blood receiving population is at risk of a generally fatal condition known as Transfusion associated graft versus host disease (TA-GVHD), which is due the presence of viable allogenic leukocytes. This syndrome is typically associated with immunosuppressed patients, such as cancer and bone marrow transplant patients, but can also occur in immunocompetent persons in the setting of restricted HLA polymorphism in the population.
Substantial attention has been devoted to finding methods to extend storage stability. One such method, for extending the storage lifetime of PCs, is recited in U.S. Pat. No. 5,466,573. This patent is directed to providing PC preparations with acetate ion sources, which acts both as a substrate for oxidative phosphorylation and as a buffer to counteract pH decrease due to lactic acid production. Such a method does not act directly on the problem of hemolysis, and membrane breakdown. An alternative method is disclosed in U.S. Pat. No. 5,496,821, commonly assigned. In this patent, whole blood is stored in a preparation including L-carnitine (LC) or alkanoyl derivatives thereof. The patent does not describe, however, the effects on blood products such as PC or RBC suspensions, and relies to at least some extent on the impact of LC on plasma characteristics.
As noted above, contamination of the blood supply with microbiological agents is another problem to be addressed by the medical community. One method of sterilizing the product, and improving reliability with respect to contamination, is to irradiate the blood product. In general, gamma irradiation values of about 25 centigray (cG), irradiating the product after it is sealed in a plastic, glass or other container is desirable. Regrettably, irradiation induces cell membrane lesions, with hemolysis in RBCs. Irradiation of blood products, including whole blood, packed RBCs and PCs continue to pose problems.
Accordingly, it remains an object of those of skill in the art to provide a method to extend the period of viability, and the circulation half-life of RBCs and PCs upon transfusion, beyond the current maximums. Additionally, it remains a goal of those of skill in the art to find a way by which blood products, including whole blood, packed RBCs and PCs can be sterilized by irradiation, without substantial membrane damage and lesions, and hemolysis.
The Applicant has discovered, through extended research, that the membrane damage experienced by RBCs and PCs upon storage, or in the face of irradiation, can be substantially delayed and suppressed, by suspending the blood product in a conventional preservation solution, such as AS-3, where the preservation solution further includes L-carnitine or an alkanoyl derivative thereof, in a concentration of 0.25-50 mM or more. Applicant""s discovery lies in the recognition that most of the decomposition of blood products, conventionally associated with decreases in ATP levels, and pH, can be in fact traced to membrane damage and hemolysis. Membrane maintenance and repair may be effected by lipid reacylation, effected, in part, through LC, the irreversible uptake of which in RBC and similar blood products has been established through the inventive research.